The present invention relates generally to navigational calculators and is more particularly concerned with a slide rule type tidal water depth calculator.
In marine navigation it is important that the vessel operator have contemporaneous knowledge of the depth of water over bottom structures in order to avoid accidental grounding thereon. This is particularly so where the vessel operates in relatively shallow waters such as, for instance is often the case in harbor operations, commercial or sport fishing, sailboat racing and the like. Commercial fisherman, for example, often operate in relatively shallow waters or are required to navigate their vessels across shallow bottom structures such as sand bars, shoals and reefs in order to reach their intended fishing grounds. It is also often of importance in commercial fishing that the crew be provided with as much actual working or "loiter" time over the fishing grounds as possible. Where a shallow bottom structure is interposed between the fishing grounds and the home port of the vessel, this "loiter" time is often severely restricted due to the fact that the draft of the vessel will not admit of traversing the shallow structure other than at times of substantial water depth. Should the vessel work too long over the fishing grounds during ebb tide, it is possible that the return trip to port cannot be safely made by the most expeditious route, in other words, directly over the intervening shallow structure. Rather, it can be found necessary to circumnavigate said structure thereby often substantially increasing the length of the trip and increasing use of fuel, refrigeration and other consumables of substantial value. Alternatively, the vessel may be required to remain over the fishing grounds until the tide once again floods sufficiently to provide safe water depth over the intervening shallow bottom structure. This expedient, however, also increases the length of the trip and the expenditure of consumables. Situations similar to the foregoing obviously also often attend the lot of the sport fisherman.
To the sailing enthusiast the depth of water under the keel is also of critical importance, particularly since sailing craft usually comprise keels of substantial depth relative to the displacement of the vessel. In sailboat racing and cruising, for instance, the chosen course for any given leg of a race or trip can be as much dictated by consideration of clearance of the keel over bottom structures as upon direction and velocity of wind and current.
In view of the foregoing, therefore, it is clearly desirable that there be provided an instrument by which the depth of water over charted structures can be readily calculated as a function of the time of the tide and/or by which the times of critical water depths relative to safe passage of a vessel over chartered structures can be quickly obtained. In accordance with the present invention, such a device has now been provided.